DLuek

Well, I disagree with stycr. A couple days/nights on Cat Ba is well worth it. Rent a motorbike and explore the island, eat seafood fresh out of the ocean and enjoy the quaint fishing village lifestyle. In my opinion it's a lot better than spending those nights in some cramped junk on Ha Long Bay with a bunch of strangers and expensive food/drink.

Unfortunately I don't have a specific answer to your question... Can't remember the name of the place we stayed a couple years ago, but there are so many decent guesthouses on the main road along the ocean. Accommodation there is also among the cheapest in the entire region. We had an A/C room with a balcony and a big window overlooking the picturesque bay for only US $7/night as I recall... Anyway it's not a hard place to find a good, cheap room.